While I, too, agree that these are probably not B-Greek questions, here are
two Web site articles by Gerhard F. Hasel, Professor of Old Testament and
Biblical Theology, Andrews University, that may help answer your questions
in part. The first article, as I skimmed it, posited some reasons for the
different readings. A diligent search of the Internet will likely turn up
other articles that relate to your questions.

> On 01/31/00, ""Grant" <grant@cajun.net>" wrote:
> B-Greek,
>
> Why does the Septuagint differ from the Masoretic text in the ages given
> within the Genesis account particularly chapter 5?
>
> What evidence is there to give support to one over the other?
> Is the LXX wrong? MT wrong? Personal opinion?
>
> Sincerely
> Grant Polle
> USA